One of the shortcomings with rigid variable direction of view endoscopes, as disclosed in U.S. Pat. No. 3,856,000 to Chikama, U.S. Pat. No. 6,371,909 to Hoeg, U.S. Pat. No. 6,560,013 to Ramsbottom, U.S. Pat. No. 4,697,577 to Forkner, U.S. Pat. No. 6,500,115 to Krattiger et al., and U.S. Pat. No. 5,762,603 to Thompson, U.S. Pat. No. 5,313,306 to Kuban, and U.S. Pat. No. 5,800,341 to McKenna et al., is their limited retrospective viewing ability. Retrospective viewing would be important in industrial or medical diagnoses because mechanical cracks or tumors sometimes develop in locations which are posterior to the endoscopic insertion port. The main reason scopes have limited retrospective viewing ability is that the endoscope shaft itself blocks an angular region around the shaft. Having the optical objective system protrude beyond the outer diameter of the shaft is not desirable because generally endoscopes must be able to slide easily in and out of guide tubes or natural lumens, and designs with retractable objective systems, as disclosed in U.S. Pat. No. 6,371,909 to Hoeg et al., are not practical. U.S. Pat. No. 6,648,817 to Schara et al. teaches a tip construction which has a swept back region of reduced cross sectional area directly behind the viewing window to allow for extreme retrospective viewing. It is designed such that the viewing window is contained within the circumference of the endoscope shaft in order to minimize the chance of the viewing window getting snagged or bumped during insertion, retraction, and use of the endoscope, but the viewing window is still relatively exposed and unshielded. Even though scope viewing windows are made of tough scratch resistant materials (sapphire), exposure is a problem, particularly in harsh applications such as inspection of industrial machines or arthroscopic surgery where the scope typically is accompanied by steel tools rotating at high rpm. Traditional fixed angle endoscopes do not have this problem because they only need the viewing window to cover a small angle and can therefore be recessed into the surrounding tip structure for maximal protection.
Accordingly, the object of the present invention is to provide variable direction of view endoscopes with a tip structure which shields the viewing window but still allows retrospective viewing. Another object of the present invention is to provide a tip structure which is less prone to getting snagged. Still further objects and advantages such as simplified construction, assembly, and alignment will become apparent from the ensuing description and drawings.